Whitewater recreationalists are persons in or on a river, rapid, or flowing channel that use the currents and various hydraulic formations for recreation and enjoyment. This grouping of recreationalists is also referred to as “boaters” or “river runners”. There are many different types of whitewater craft that whitewater recreationalists can use to make their way down a river or rapid. An abbreviated list includes:
Inflateable kayaksOpen-deckedRaftsKayaksand other craftCanoesClosed-deckedDory or DriftPersonal InflatedCataraftsCanoesBoatsWater Craft (“rubberduckies”)Wake boards &Swimmers withSurfboards &Tubesother smallor without fins,Riverboardsboards used toand paddlesassistswimming
Whitewater recreationalists include an increasing number of persons with disabilities including paraplegics, the blind, amputees, etc. Organized sports which involve or evolved from recreational whitewater include:                Slalom: A competitive event for canoeing and kayaking where boaters negotiate gates suspended over the river for the fastest time.        Freestyle or Rodeo: A competitive event for canoeing and kayaking where boaters perform tricks on a wave, hole, or other hydraulic feature or obstruction.        Rafting: An event where rafters race down the river for the fastest time.        Down-River or Wildwater kayaking: An event where kayakers race down the river for the fastest time.        Squirt Boating: A competitive event where kayakers and canoeists perform tricks utilizing sub-surface current in low volume boats.        
Open Channel Hydraulics is the formalized science that considers the formation of hydraulic formations that are encountered by whitewater recreationalists found in rivers and man-made structures. This includes those features associated with whitewater rapids and features. The basic equations governing whitewater hydraulic formations are the Navier-Stokes equations which are an application of Newton's second law. These can be reduced to simpler forms when considering the free (water) surface found in rivers and channels and the incompressibility of water.
Whitewater recreationalists refer to various hydraulic formations found in fast-moving rivers, rapids, and channels. These hydraulic formations include “Holes”, “Waves”, and “Hydraulics”. These describe various forms of what is referred to by scientists and engineers as a hydraulic jump. (Note however that waves can be formed by other hydraulic mechanisms.) A hydraulic jump occurs when fast moving flow in a state known as supercritical changes to a slower moving subcritical state. From a scientific point of view, supercritical flow is defined as having a Froude Number greater than one, and subcritical flow is defined as having a Froude Number less than one. The Froude Number is a well defined hydraulic term which is a dimensionless ratio of inertial forces to gravitational forces. The Froude Number is defined as V_√(gd), where V=velocity of the flow, g=gravitational acceleration, and d=characteristic depth.
The hydraulic jump was studied extensively in the 1950s and 1960s, although hydraulic jump formations involving non-linear channel geometries formations can be quite complex and difficult to analyze or predict—even with computer modeling. Physical structures that can create waves and holes with recreationally desirable attributes have a vertical or steep downward slope in the vicinity where the hydraulic jump occurs. This condition was studied in the 1950s and 1960s and is know as a hydraulic jump at an abrupt drop.
The abrupt drop can cause the hydraulic jump to stabilize in deeper areas, and create other characteristics that are advantageous to whitewater recreationalists. At an abrupt drop the transition from supercritical to subcritical flow is characterized by several flow patterns depending upon the inflow and conditions found in the downstream pool (tailwater). These flow patterns include (1) the A-jump, (2) the wave jump or W-jump or the wave train, and (3) the B-jump which is characterized by a plunging jet. The characteristics of wave jump and wave train are essentially the same and hereafter the wave jump and wave train will simply be referred to as ‘Wave’
Holes and waves are often the predominant features treasured by whitewater recreationalists. Holes are more retentive—having tendency to impede the passage of buoyant objects, while waves create exciting changes in elevation. Waves known as “breaking waves” can also have breaking water (whitewater) toward their crest that acts to retain buoyant whitewater craft. The form and type of these hydraulic jumps varies dramatically and even small nuances not noticeable to the untrained eye can affect the desirability to whitewater recreationalists.
Pools are areas in a river or channel that move slowly (relative to the higher velocity rapids) in the downstream direction. They are typically in a hydraulic state known as subcritical—having a Froude Number less than a value of one. However higher velocity currents or jets can carry through the entire length of a pool. Pools can also have recirculating eddy currents known as “eddies”. Pools are advantageous to whitewater recreationalists for recovery.
Eddies are formed upstream and downstream of obstructions in a river. Eddies are generally recognized by whitewater recreationalists to occur in a pool adjacent to and downstream of a wave or hole. Eddies are currents that tend to rotate in the horizontal plane. This rotation can usually be seen on the surface of the water. Typically, the flow in an eddy is oriented upstream rather than downstream. An eddy can have slow or mild upstream currents or can be quite violent. The characteristics of an eddy are important to the recreational experience of whitewater recreationalists playing in an adjacent hydraulic jump.
Structures that create the various formations of the hydraulic jump including waves and holes tend to control and focus flow and/or lower the flow to increase it's velocity and power so that it is supercritical. This requires some type of crest, which usually has elevated portions to form a constriction. The flow in the vicinity of the physical crest—also known as a control section—typically enters a state known as critical depth. Note that at this location, the Froude Number of the flow has a value of one. Downstream of this crest is a ramp where the flow transitions from a critical state to supercritical state prior to entering the hydraulic jump. Note that some structures have an entirely vertical ramp; while in others; there is no clear physical distinction between the crest and the ramp. The ramp is simply where the flow transitions from the critical flow to the hydraulic jump.
A wave can also be created in situations where a hydraulic jump is not involved. Sometimes known as a wave train or standing waves, these can be created by a perturbation or series of perturbations or “bumps” in the invert of a river or channel. This type of wave, however, is difficult to reliably create or predict and usually occurs through very specific flow rates when found in natural rivers.
Typically, prior art man made physical structures for producing hydraulic formations have fixed geometries and fixed dimensions. One problem with these fixed physical structures is that they may not produce the desired hydraulic formations at normal or low water flow rates. In addition, at excessively high water flow rates, fixed physical structures may form constrictions, increased floodplains and high water surface elevations.
It would be advantageous for physical structures for producing hydraulic formations to have an adjustable geometry, which could be used to vary the size and character of the corresponding hydraulic formations over a wide range of water flow rates. It would also be advantageous for physical structures for producing hydraulic formations to be adjustable for constructing a variety of systems for whitewater recreationalists under a variety of conditions.
Various embodiments of adjustable physical structures to be further described can be used to form hydraulic formations. In addition, the adjustable physical structures can be adjusted to vary the geometry of the hydraulic formations, and can be used over a wide range of flow rates and environmental conditions. Further, the adjustable physical structures can be used to construct various systems including kayak courses, rafting courses, boating courses and theme park rides.
However, the foregoing examples of the related art and limitations related therewith, are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.